Antenna

ABSTRACT

An antenna comprises a base member ( 3 ), a ground conductor ( 5 ), a first antenna element ( 7 ) and a second antenna element ( 9 ). The base member ( 3 ) is formed in a thin plate shape and made of dielectric material. The ground conductor ( 5 ) is formed of a thin-film shaped and rectangular conductor and disposed on the base member ( 3 ). The first antenna element ( 7 ) is formed of a thin-film shaped and L-shaped conductor, is disposed on the base member ( 3 ) and has one end connected to one end ( 5 A) of the ground conductor ( 5 ). The second antenna element ( 9 ) is formed of a thin-film shaped and rectangular conductor and is disposed on the base member ( 3 ) to be isolated from the ground conductor ( 5 ) and the first antenna element ( 7 ).

TECHNICAL FIELD

The present invention relates to antennas for use in radio communicationapparatuses such as a portable telephone, PDA and wireless LAN and, moreparticularly, to a film antenna.

BACKGROUND ART

Recently, radio communication apparatuses such as a portable telephone,PDA (Personal Digital Assistants) and wireless LAN are daily employed.Since the radio communication apparatuses are designed on a premise thatthese are carried by users at all times, these apparatuses tend to beminiaturized and formed in a thin structure. With such a tendency,component parts, to be installed in the radio communication apparatuses,have similar tendencies.

In recent radio communication, there are increasing cases where aplurality of frequency bands are utilized. For example, the wireless LANutilizes wavelengths in 2.4 GHz and 5 GHz bands. For this reason, theantennas for use in the radio communication apparatuses are required tobe usable at a plurality of separate frequency bands.

A notebook-sized PC and a portable telephone use an inverted-F antenna,a dielectric antenna or a substrate antenna as built-in antenna. Theseantennas have features such as omnidirections and high-gains.

However, due to limited conditions in structure, it is hard to minimizethe antenna in size and, especially, to form the antenna in a thinstructure. When the antenna is installed in the notebook-sized PC, theantenna must be disposed in a limited area, such as a position near ahinge or a frame portion of an LCD (Liquid Crystal Display) because manyof the component parts are densely located inside the notebook-sized PC.

Further, the inverted-F antenna of the related art has inherent problemslisted below.

As one of the inverted-F antennas of the related art, an antenna whichis disclosed in Japanese Patent Provisional Publication No. 2000-68737has been known. The inverted-F antenna 100 is formed by folding ametallic plate 102 into a substantially U-shaped configuration as shownin FIG. 1. The inverted-F antenna 100 is available to be placed in anarrow space and can be manufactured in a low conducting loss and lowcost. An inner conductor 132 of a coaxial cable 130 is electricallyconnected to a radiating portion 102 a of the metallic plate 102. Anouter conductor 134 of the coaxial cable 130 is electrically connectedto a ground portion 102 b of the metallic plate 102.

In order to operate the inverted-F antenna 100 in a plurality offrequency bands, an antenna 110 in which the inverted-F antenna 100 isprovided with a parasitic circuit body 104 as shown in FIG. 2 has beenknown. The antenna 110 comprises the metallic plate 102, the parasiticcircuit body 104 and a spacer 106. The parasitic circuit body 104 isdisposed on an upper surface of the spacer 106. The spacer 106 is madeof dielectric material (non-conductor) and inserted between theradiating portion 102 a and the ground portion 102 b. Under such astructure, if the inner conductor 132 of the coaxial cable 130 iselectrically connected to the radiating portion 102 a and the outerconductor 134 of the coaxial cable 130 is electrically connected to theground portion 102 b, the radiating portion 102 a and the parasiticcircuit body 104 generate a first resonant frequency and a secondresonant frequency, respectively.

When the spacer 106 is disposed on the metallic plate 102, it isgenerally hard to precisely match a distance between the metallic plate102 and the spacer 106 to a given length. For this reason, the distancebetween the radiating portion 102 a and the parasitic circuit body 104can not be accurately adjusted into a given length. As a result, theantenna 110 can not obtain accurate resonant frequencies becauseelectrical capacitance between the radiating portion 102 a and theparasitic circuit body 104 deviates from a given value. In a case wherethe resonant frequency generated by the antenna 110 increases, thisproblem becomes more serious.

An antenna 120 is a modified form of the antenna 110. As shown in FIG.3, the antenna 120 has the same structure as the antenna 110 except fora shape in which a spacer 122 is different from the spacer 106. Theantenna 120 is smaller than the antenna 110 because the spacer 122 isentirely accommodated in a space between the radiating portion 102 a andthe ground portion 102 b of the metallic plate 102. However, the antenna120 can not obtain accurate resonant frequencies because it is difficultto precisely match the distance between the radiating portion 102 a andthe parasitic circuit body 104 to a given length.

Also, the above problems arise in a case where a plurality of parasiticcircuit bodies are provided to generate a plurality of resonantfrequencies.

DISCLOSURE OF INVENTION

The present invention has been completed with the above view in mind andhas an object to provide an antenna capable of being placed in a narrowspace and of easily obtaining a plurality of accurate resonantfrequencies each which belongs to a separate frequency band.

To achieve the above object, the present invention provides an antennacomprising: a thin plate-like base member made of dielectric material; aground conductor formed of a thin-film shaped and rectangular conductorand disposed on the base member; a first antenna element formed of athin-film shaped and L-shaped conductor, having one end connected to oneend of the ground conductor and disposed on the base member; and asecond antenna element formed of a thin-film shaped and rectangularconductor and disposed on the base member without being directlyconnected to the ground conductor and the first antenna element.

According to the present invention, the antenna can be placed in anarrow space because the film-like antenna can be manufactured byforming the ground conductor, the first antenna element and the secondantenna element on the base member. If an inner conductor, an outerconductor and a sheath of a coaxial cable are connected to the firstantenna element, the ground antenna element and the second antennaelement, respectively, and then alternating-current electricity flowsinto the coaxial cable, a first resonant frequency and a second resonantfrequency are generated on the first antenna element and the secondantenna element, respectively. Therefore, the antenna of the presentinvention has a capability of easily obtaining two resonant frequencieseach belonging to a separate frequency band.

To achieve the above object, the present invention provides an antennacomprising: a thin plate-like base member made of dielectric material; afirst antenna element formed of a thin-film shaped conductor anddisposed on the base member so as to form a slit portion opening at apart thereof; a second antenna element formed of a thin-film and stripshaped conductor and disposed in the slit portion; and an impedanceadjustment element formed of a thin-film and strip shaped conductor anddisposed between one side of the first antenna element and the secondantenna element in the slit portion.

According to the present invention, the antenna can be placed in anarrow space because the film-like antenna can be manufactured byforming the first antenna element, the second antenna element and theimpedance adjustment element on the base member. If an inner conductor,an outer conductor and a covering material of a coaxial cable areconnected to a part of the first antenna element, a part of the secondantenna element and the impedance adjustment element, respectively, andthen alternating-current electricity flows into the coaxial cable afterimpedance is adjusted by means of the impedance adjustment element, afirst resonant frequency and a second resonant frequency are generatedon the first antenna element and the second antenna element,respectively. Therefore, the antenna of the present invention has acapability of easily obtaining two resonant frequencies each belongingto a separate frequency band.

To achieve the above object, the present invention provides an antennacomprising: a thin plate-like base member made of dielectric material; afirst antenna element formed of a thin-film shaped conductor anddisposed on the base member so as to form a slit portion opening at apart thereof; and a second antenna element formed of a thin-film andstrip shaped conductor and disposed in the slit portion.

According to the present invention, the antenna can be placed in anarrow space because the film-like antenna can be manufactured byforming the first antenna element and the second antenna element on thebase member. If an inner conductor, an outer conductor and a sheath of acoaxial cable are connected to one part of the first antenna element,the second antenna element and another part of the first antennaelement, respectively, and then alternating-current electricity flowsinto the coaxial cable, a first resonant frequency and a second resonantfrequency are generated on the first antenna element and the secondantenna element, respectively. Therefore, the antenna of the presentinvention has a capability of easily obtaining two resonant frequencieseach belonging to a separate frequency band.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a schematic structure of aninverted-F antenna of the related art.

FIG. 2 is a perspective view showing a schematic structure of theinverted-F antenna of the related art in which a parasitic circuit bodyis provided.

FIG. 3 is a perspective view showing another schematic structure of theinverted-F antenna of the related art in which a parasitic circuit bodyis provided.

FIG. 4 is a plan view of a two-resonance antenna according to a firstembodiment of the present invention.

FIG. 5 is a cross sectional view of a coaxial cable according to thefirst embodiment of the present invention.

FIG. 6 is a view illustrating a VSWR characteristic of the two-resonanceantenna according to the first embodiment of the present invention.

FIG. 7A is a view illustrating a radiating characteristic of thetwo-resonance antenna according to the first embodiment of the presentinvention.

FIG. 7B is a view illustrating a rotative direction of the two-resonanceantenna according to the first embodiment in FIG. 7A.

FIG. 8 is a schematic illustrative view of the two-resonance antennaaccording to the first embodiment of the present invention mounted on anLCD section of a notebook-sized PC.

FIG. 9 is a perspective view of the two-resonance antenna according tothe first embodiment of the present invention in a folded status.

FIG. 10 is a perspective view of the two-resonance antenna shown in FIG.9 mounted on a corner area of a case of the notebook-sized PC.

FIG. 11 is a perspective view of the two-resonance antenna according tothe first embodiment of the present invention applied to a supportmember.

FIG. 12A is a view illustrating a first modified form of thetwo-resonance antenna according to the first embodiment of the presentinvention.

FIG. 12B is a view illustrating a second modified form of thetwo-resonance antenna according to the first embodiment of the presentinvention.

FIG. 12C is a view illustrating a third modified form of thetwo-resonance antenna according to the first embodiment of the presentinvention.

FIG. 13 is a plan view of a two-resonance antenna according to a secondembodiment of the present invention.

FIG. 14 is a view illustrating actual sized of antenna elements used inthe two-resonance antenna according to the second embodiment of thepresent invention.

FIG. 15 is a view illustrating a VSWR characteristic of thetwo-resonance antenna according to the second embodiment of the presentinvention.

FIG. 16A is a view illustrating a radiating characteristic of thetwo-resonance antenna according to the second embodiment of the presentinvention.

FIG. 16B is a view illustrating a rotative direction of thetwo-resonance antenna according to the second embodiment in FIG. 16A.

FIG. 17 is a schematic illustrative view of the two-resonance antennaaccording to the second embodiment of the present invention mounted onan LCD section of a notebook-sized PC.

FIG. 18 is a perspective view of the two-resonance antenna according tothe second embodiment of the present invention mounted on a corner areaof a case of the notebook-sized PC.

FIG. 19 is a perspective view of the two-resonance antenna according tothe second embodiment of the present invention applied to a supportmember.

FIG. 20 is a modified form of the two-resonance antenna according to thesecond embodiment of the present invention.

FIG. 21 is a plan view of a two-resonance antenna of a third embodimentaccording to the present invention.

FIG. 22 is a view illustrating a VSWR characteristic of thetwo-resonance antenna according to the third embodiment of the presentinvention.

FIG. 23A is a view illustrating a radiating characteristic of thetwo-resonance antenna according to the third embodiment of the presentinvention.

FIG. 23B is a view illustrating a rotative direction of thetwo-resonance antenna according to the third embodiment in FIG. 19A.

FIG. 24 is a plan view of a two-resonance antenna according to a fourthembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, with reference to FIGS. 4 to 24, first to fourthembodiments according to antenna of the present invention are described.

First Embodiment

FIG. 4 is a plan view of a two-resonance antenna 1. In the presentembodiment, a major axis and a minor axis of a base member 3 areassigned to an X-axis and a Y-axis, respectively, and the X-axis andY-axis perpendicularly cross each other.

The two-resonance antenna 1 is a monopole antenna formed in a film shapeand comprises a base member 3, a ground conductor 5, a first antennaelement 7 and a second antenna element 9. The base member 3 is formed ofa rectangular thin plate with flexibility and is made of dielectricmaterial such as resin of a polyamide system. The ground conductor 5,the first antenna element 7 and the second antenna element 9 are formedon a surface of the base member 3. The ground conductor 5, the firstantenna element 7 and the second antenna element 9 take the forms ofconductors each which is formed in a thin film shape and is made ofmetal such as beaten-copper.

The ground conductor 5 is formed along the X-axis and serves as arectangular grand surface in the monopole antenna. In order to generateelectric images of the first antenna element 7 and the second antennaelement 9 on the ground conductor 5, the ground conductor 5 has a largersurface area than those of the first antenna element 7 and the secondantenna element 9.

The first antenna element 7 is formed in an L-shaped configuration withtwo combined rectangular conductors (including a short-circuited portion7A and a radiating portion 7B). The short-circuited portion 7A of thefirst antenna element 7 is connected to one end 5A of the groundconductor 5. The radiating portion 7B of the first antenna element 7 isshorter than the ground conductor 5 and is disposed in parallel to theground conductor 5. With such a layout, a slit portion 6 having an openat one end thereof is formed on the base member 3.

Although the first antenna element 7 of the present embodiment has thelayout in which the short-circuited portion 7A is perpendicularlycontiguous with the radiating portion 7B, the present invention is notlimited to such a layout and may take a contiguous configuration in anobtuse angle or an acute angle. Also, although the first antenna element7 of the present embodiment has the layout in which a side wall of theshort-circuited portion 7A is formed in a straight-line configuration,the present invention is not limited to such a layout and may take aconfiguration formed in a circular arc. When the side wall of theshort-circuited portion 7A is formed in the circular arc configuration,the ground conductor 5 and the first antenna element 7 form a conductorin a substantially U-shaped configuration on the base member 3.

The second antenna element 9 is formed in a rectangular shape. Thesecond antenna element 9 is disposed in the slit portion 6 so as to liein parallel to the ground conductor 5 and the radiating portion 7B ofthe first antenna portion 7. The second antenna 9 is shorter than theground conductor 5 and the radiating portion 7B of the first antennaportion 7.

FIG. 5 is a cross sectional view of a coaxial cable 11. The coaxialcable 11 comprises a center conductor 13, a covering material 15, anouter conductor 17 and a sheath 18. The center conductor 13 is coveredwith the covering material 15. The outer conductor 17 is disposed aroundan outer periphery of the covering material 15 and is covered with thesheath 18 which is made of insulation material (dielectric material).The sheath 18 serves to protect the outer conductor 17 and isolate theouter conductor 17 from an outside of the coaxial cable 11.

As shown in FIG. 4, a first connecting portion 7C is formed on a part ofthe radiating portion 7B of the first antenna portion 7 in order toelectrically connect the first antenna element 7 to the center conductor13 of the coaxial cable 11 by direct-current electricity. A contactportion 9A is formed on a part of the second antenna portion 9 in orderto electrically connect the second antenna element 9 to the outerconductor 17 of the coaxial cable 11 by alternating-current electricityvia the sheath 18 of the coaxial cable 11. A second connecting portion5B is formed on a part of the ground conductor 5 in order toelectrically connect the ground conductor 5 to the outer conductor 17 ofthe coaxial cable 11 by direct-current electricity. The first connectingportion 7C, the second connecting portion 5B and the contact portion 9Aare located on a straight line along the Y-axis.

The center conductor 13 exposed at a terminal portion of the coaxialcable 11 is connected to the first connecting portion 7C by soldering.Removing the sheath 18 by a given length in a longitudinal direction ofthe coaxial cable 11 allows the outer conductor 17, exposed on thecoaxial cable 11, to be connected to the second connecting portion 5B bysoldering. The outer conductor 17 covered with the sheath 18 is fixed tothe contact portion 9A by contact or an adhesive. Since the outerconductor 17 is not directly connect to the second antenna element 9, noelectric current flows between the second antenna element 9 and theouter conductor 17 even when applied with direct-current electricity.With such a structure, there is no need to separately provide aparticular member for avoiding the second antenna element 9 and theouter conductor 17 from directly contacting each other, resulting in thetwo-resonance antenna 1 with a simplified structure.

The second antenna element 9 is isolated from the center conductor 13 ofthe coaxial cable 11, the outer conductor 17 of the coaxial cable 11,the first antenna element 7 and the ground conductor 5. However, thesecond antenna element 9 is capacitively coupled with the groundconductor 5 and the first antenna element 7 through the base member 3made of dielectric material. Further, the second antenna element 9 iscapacitively coupled with the outer conductor 17 of the coaxial cable 11via the sheath 18. This arrangement is equivalent to an arrangement inwhich the second antenna element 9 is connected to the ground conductor5, the first antenna element 7 and the outer conductor 17 via acapacitor. Accordingly, if alternating-current electricity is applied tothe center conductor 13 of the coaxial cable 11, electric current flowsbetween the ground conductor 5 and the second antenna element 9, betweenthe first antenna element 7 and the second antenna element 9 and betweenthe second antenna element 9 and the outer conductor 17. Here, it isnoted that electric current flowing between the ground conductor 5 andthe second antenna element 9 almost never contributes to resonance ofthe second antenna element 9.

In order to adjust electrical capacitance between the contact portion 9Aand the outer conductor 17, a film-shaped dielectric member may bedisposed between the sheath 18 and the contact portion 9A. Thisdielectric member allows a resonant frequency, which would be generatedon the second antenna element 9, to be easily adjusted.

Next, a resonance principle of the two-resonance antenna 1 is describedbelow.

First resonance of the two-resonance antenna 1 is generated by electriccurrent distributed on the first antenna element 7. Namely, thisresonance is generated by a first inverted-F antenna formed of the firstantenna element 7. A resonance principle of the first inverted-F antennais the same as that of a λ/4 monopole antenna. A length of the firstantenna element 7 is about one fourth of the wavelength of the firstinverted-F antenna. Impedance matching which causes the first inverted-Fantenna to generate the resonant frequency is carried out by changing aconnecting position of the center conductor 13 of the coaxial cable 11.

Second resonance of the two-resonance antenna 1 is generated by electriccurrent distributed on the second antenna element 9 and outer conductor17 of the coaxial cable 11. Namely, this resonance is generated by asecond inverted-F antenna formed of the second antenna element 9 and theouter conductor 17. A resonance principle of the second inverted-Fantenna is the same as that of a λ/2 antenna. If alternating-currentelectricity is supplied from the center conductor 13 of the coaxialcable 11 to the first antenna element 7, first electric current flows onthe second antenna element 9 because the first antenna element 7 iscapacitively coupled with the second antenna element 9. The firstelectric current is distributed on the second antenna element 9. Secondelectric current flows on the outer conductor 17 because the secondantenna element 9 is capacitively coupled with the outer conductor 17.The second electric current flows to a GND surface of the groundconductor 5 through the second connecting portion 5B. A total lengthgiven by adding a length of the second antenna element 9 to a lengthbetween the contact portion 9A and the second connecting portion 5B inthe outer conductor 17 is about one second of the wavelength of thesecond inverted-F antenna. Impedance matching which causes the secondinverted-F antenna to generate the resonant frequency is carried out bychanging a thickness of the sheath 18 intervening between the secondantenna element 9 and the outer conductor 17. Therefore, in the secondinverted-F antenna, it is important not to electrically contact thesecond antenna element 9 to the outer conductor 17 by means of theinsulation layer such as the sheath 18.

The two-resonance antenna 1 has a VSWR characteristic shown in FIG. 6and a radiating characteristic shown in FIG. 7A.

The VSWR (Voltage Standing Wave Ratio) is described below in detail. Ina state of connecting an electric power supply line to the antenna, whenalternating-current electricity flows in the electric power supply line,electric current flows on the antenna. Voltage vibration generated onthe electric power supply line by the electric current is termed aprogressive wave. If there is a difference between a characteristicimpedance of the electric power supply line and a characteristicimpedance of the antenna, electric current is reflected at a point wherethe electric power supply line is connected to the antenna, which causessome of the electric current to return to a transmission side. Voltagevibration generated on the electric power supply line by the returnedelectric current is termed a reflected wave. In general, if there is thereflected wave on the electric power supply line, an electric power lossoccurs at the point where the electric power supply line is connected tothe antenna. Therefore, the characteristic impedance of the electricpower supply line and the characteristic impedance of the antenna aremutually adjusted so as to have the same values to suppress a generationof reflected wave as less as possible. If there are the progressive waveand the reflected wave on the electric power supply line, two waves aresynthesized to form a standing wave. A ratio between the maximumamplitude and the minimum amplitude of the standing wave is termed VSWR.The VSWR and a power loss rate (reflected power) R are respectivelydefined by Eqs. (2) and (3) by using a reflection coefficient |Γ|defined by Eq. (1).Γ=(Zi−Z0)/(Zi+Z0)  (1)VSWR=(1+|Γ|)/(1−|Γ|)  (2)R=|Γ|²×100  (3)where Zi is the characteristic impedance of a line (electric powersupply line), and Z0 is the characteristic impedance of a load(antenna).

For example, if the coaxial cable 11 with 50 Ω resistor is connected toa dipole antenna with 75 Ω resistor, |Γ|=0.2, VSWR=1.5 and R=4 arederived from the above Eqs. Accordingly, electric power is reflected ata rate of 4% from an electric power supply point of an antenna.

If the characteristic impedance of the electric power supply line andthe characteristic impedance of the antenna have the same values, thereflection coefficient and the VSWR have the values of 0 and 1,respectively. In this case, the reflection loss of the electric powerdoes not occur at the electric power supply point because the electricpower reflection has the value of 0. From Eqs. (2) and (3), if the valueof the VSWR becomes larger, the reflection loss of the electric powerbecomes larger at the electric power supply point. From the reasonsdiscussed above, in fabrication of the antenna, the characteristicimpedance of the electric power supply line and the characteristicimpedance of the antenna are adjusted such that the VSWR has the valueof 1 as close as possible.

In FIG. 6, there are two band widths appearing at two regions with afrequency in which the VSWR has a value less than “2”. One of theseregions lies in a value ranging from 2.2 GHz to 2.9 GHz. The other ofthese regions lies in a value ranging from 5.1 GHz to 5.2 GHz.Accordingly, the band widths correspond to a range of approximately 700MHz at 2 GHz band and to a range of approximately 100 MHz at 5 GHz band.

Next, the radiating characteristic is described below in detail. Theelectric power supplied from the electric power supply line is lost inthe form of heat which is generated by the material forming the antennabefore the electric wave is radiated. Also, depending on the shape ofthe antenna, a radiating pattern of the antenna varies. Therefore, inorder to understand a performance of the antenna, the electric powerloss (a gain availability) and the radiating pattern (a directivity) ofthe antenna are grasped by researching gains of the antenna in anomnidirectional range while the antenna is rotated as shown in FIG. 7B.

As shown in FIG. 7A, in 2 GHz and 5 GHz bands, vertical polarized wavesforming main polarized waves have shapes nearly equal to circularconfigurations and have high-gain availabilities. Accordingly, thetwo-resonance antenna 1 has omnidirection and high-gain availabilitythat are desired characteristics of the antenna.

The two-resonance antenna 1 has advantageous features listed below.

The first resonant frequency and the second resonant frequency can befreely set to arbitrary values, respectively, because the first antennaelement 7 on which the first resonant frequency is generated and thesecond antenna element 9 on which the second resonant frequency isgenerated are disposed to be independent from each other. For example,both resonant frequencies can be adjusted such that a difference betweenthe first resonant frequency and the second resonant frequencyincreases.

Impedance adjustment between the two-resonance antenna 1 and the coaxialcable 11 can be easily performed because the first connecting portion7C, the second connecting portion 5B and the contact portion 9A can beset to respective positions independent from one another.

The coaxial cable 11 can be easily fixed to the two-resonance antenna 1because the first connecting portion 7C, the second connecting portion5B and the contact portion 9A are disposed on the surface of the basemember 3. In addition, the coaxial cable 11 can be easily fixed to thetwo-resonance antenna 1 without bending because the first connectingportion 7C, the second connecting portion 5B and the contact portion 9Aare linearly located.

The antenna can be realized in a miniaturized and thin structure becausethe two-resonance antenna 1 is fabricated by combining the L-shapedfirst antenna element 7 and the rectangular ground conductor 5, formingthe slit portion 6 which opens at one end thereof, and locating therectangular second antenna element 9 in the slit portion 6.

Electrical capacitances between the second antenna element 9 and thefirst antenna element 7 and between the second antenna element 9 and theground conductor 5 can be easily ensured such that they have respectivelarge values because the second antenna element 9 is formed in anelongated state in substantially parallel to and along the first antennaelement 7 and the ground conductor 5 and is formed inside the firstantenna element 7 and the ground conductor 5.

Noises occurring in the two-resonance antenna 1 are absorbed by theouter conductor 17 because the coaxial cable 11 in which the outerconductor 17 is disposed around the center conductor 13 is employed asthe electric power supply line for the antenna. Accordingly, thetwo-resonance antenna 1 is hard to suffer from an adverse affect causedby the noises.

A simplification in an antenna structure and reduction in manufacturingcost can be realized because the two-resonance antenna 1 is manufacturedby forming the first antenna element 7 and the second antenna element 9in thin film metallic elements on the surface of the base member 3 madeof the dielectric material of the polyamide system.

As one of manufacturing methods of the two-resonance antenna 1, thetwo-resonance antenna 1 may be manufactured by means of an etchingtechnique by using CCL and a screen printing technique. According tothis method, a shape of the ground conductor 5, a shape of the firstantenna element 7, a shape of the second antenna element 9, a relativeposition between the ground conductor 5 and the second antenna element9, and a relative position between the first antenna element 7 and thesecond antenna element 9 can be precisely fixed on the base member 3because the ground conductor 5, the first antenna element 7 and thesecond antenna element 9 are formed on the base member 3 in a singlestep. Consequently, electrical capacitances between the ground conductor5 and the second antenna element 9 and between the first antenna element7 and the second antenna element 9 can be maintained in respectiveaccurate values, and it is possible to perform mass production of thetwo-resonance antenna 1 within a short period of time. Also, reductionin a pre-investment and flexibility in shape of the antenna can berealized because no metal mold is required for manufacturing thetwo-resonance antenna 1.

Next, a method for installing the two-resonance antenna 1, as an antennafor a wireless LAN compatible with two-frequencies, on a notebook-sizedPC 19 is described below.

As shown in FIG. 8, when the two-resonance antenna 1 is mounted on anLCD section 20 of the notebook-sized PC 19, a portion of the base member3 of the two-resonance antenna 1 is superposed on a rear wall of an LCDpanel 23, and the two-resonance antenna 1 is fixedly secured to a frameportion of the LCD section 20 through an two-sided tape. In general, inorder to form the notebook-sized PC 19 in a thin structure, the LCDsection 20 is designed to be extremely thin. Since a thickness of thetwo-resonance antenna 1 is extremely thin in the order of approximately100 μm, there is not a problem that the thickness of the LCD section 20increases by placement of the two-resonance antenna 1.

As shown in FIG. 10, in a case where the two-resonance antenna 1 ismounted on a corner area of a casing 21 of the notebook-sized PC 19, thetwo-resonance antenna 1 is folded and then secured to the corner area ofthe casing 21 of the notebook-sized PC 19 through a two-sided tape.Since the two-resonance antenna 1 is a basal plate composed of the basemember 3 which is thin and has flexibility, the antenna can be folded.In particular, as shown in FIG. 9, the base member 3 is divided into avertical section 25 and a horizontal section 27 with respect to a linesegment L, and the vertical section 25 vertically extends in a directionalong the +Z-axis with respect to the horizontal section 27. Thevertical section 25 includes one part of the short-circuited portion 7Aof the first antenna element 7, the radiating portion 7B of the firstantenna element 7 and the second antenna element 9. The horizontalsection 27 includes the other part of the short-circuited portion 7A ofthe first antenna element 7 and the ground conductor 5. With such astructure, the two-resonance antenna 1 can be located at the corner areaof the casing 21 of the notebook-sized PC 19.

Next, a method for applying the two-resonance antenna 1 to a supportmember 33, as a two-resonance antenna device, is described.

FIG. 11 is a perspective view of the two-resonance antenna device 31.Also, in the present embodiment, a longitudinal direction, a lateraldirection and a vertical direction of the support member 33 are assignedto an X-axis, a Y-axis and a Z-axis, respectively, and the X-axis, theY-axis and the Z-axis perpendicularly cross one another. Thetwo-resonance antenna device 31 comprises the two-resonance antenna 1and the support member 33. Also, the base member 3, the ground conductor5, the first antenna element 7 and the second antenna 9 haveflexibilities.

The support member 33 has rigidity and is made of non-conductivematerial (insulation material) such as resin or ceramic. The supportmember 33 is integrally formed of an upper end portion 35, aninterconnecting portion 37 and a lower end portion 39. Longitudinal axesof the upper end portion 35 and the lower end portion 39 extend alongthe X-axis, and lateral axes of these components extend along theY-axis. A distal end 35A of the upper end portion 35 is located on a −Xside with respect to a distal end 39A of the lower end portion 39. Alongitudinal axis of the interconnecting portion 37 extends along theZ-axis, and a lateral axis of this component extends along the Y-axis.One end of the interconnecting portion 37 is connected to a base endportion 35B of the upper end portion 35, and the other end of theinterconnecting portion 37 is connected to a base end portion 39B of thelower end portion 39.

A length of the base member 3 is set to equal a total length of theupper end portion 35, the interconnecting portion 37 and the lower endportion 39 of the support member 33. The base member 3 and the supportmember 33 are fixed to each other by means of a two-sided tape oradhesive. In a state of fixing the base member 3 to the support member33, the base member 3 is disposed on an outside surface of the supportmember 33. The ground conductor 5, the first antenna element 7 and thesecond antenna element 9 are foldable depending on a folded status ofthe base member 3. Also, the base member 3 may be provided with rigidityand used as a support in place of the support member 33.

The two-resonance antenna device 31 has advantageous features listedbelow.

Even if displacement occurs in a relative position between the supportmember 33 and the base member 3 at a time of applying the base member 3on the support member 33, no changes occurs in the shape of the groundconductor 5, the shape of the first antenna element 7, the shape of thesecond antenna element 9, the relative position between the groundconductor 5 and the second antenna element 9 and the relative positionbetween the first antenna element 7 and the second antenna element 9.

An occupied area of the two-resonance antenna device 31 can be minimizedbecause the base member 3 is formed on the three-dimensional basis.

The two-resonance antenna device 31 is available to be placed in anarrow space and to easily obtain two accurate resonant frequencies.Also, radiation and receipt of three-dimensional waves can be favorablyaccomplished because the base member 3 is formed on thethree-dimensional basis.

The two-resonance antenna device 31 can be easily altered in shape bychanging the shape of the support member 33 without altering the shapeof the base member 3.

By using an etching technique, the ground conductor 5, the first antennaelement 7 and the second antenna element 9 are formed on the base member3. Therefore, the shapes and the positions of the respective conductiveelements can be precisely maintained and each of the conductive elementscan be set to have a width less than 1 mm. In addition, each of theconductive elements can be freely formed in a desired shape, andimprovement in mass productivity and reduction in manufacturing costscan be realized.

The base member 3, the ground conductor 5, the first antenna element 7and the second antenna element 9 become hard to deform because the basemember 3 is fixed on the support member 33. Therefore, the two-resonanceantenna device 31 can be easily handled and maintain the resonantfrequencies at given values.

If the base member 3 is fixed on the support member 33 such that thesurfaces on which the respective conductive elements are placed is heldin contact with the support member 33, the respective conductiveelements become hard to be damaged because they do not appear on thesurface of the two-resonance antenna device 31.

A mass of the two-resonance antenna device 31 is reduced because thesupport member 33 is formed of resin or ceramics. Also, thetwo-resonance antenna device 31 can easily secure compatibility with theinverted-F antenna of the related art because the two-resonance antenna31 is formed in the same shape as that of an inverted-F antenna of therelated art.

Since the base member 3 is applied onto the surface of the supportmember 33, application work of the base member 3 can be easily performedand manufacturing work of the two-resonance antenna device 31 can beeasily accomplished.

If the sheath 18 of the coaxial cable 11 is used to prevent the secondantenna element 9 from directly contact to the center conductor 13 orthe outer conductor 15 of the coaxial cable 11, the two-resonanceantenna device 31 can be constructed without separately preparing othermembers having insulating properties.

Further, the support member 33 and the base member 3 may be suitablyaltered in shape. Also, the ground conductor 5, the first antennaelement 7 and the second antenna element 9 which are formed on the basemember 3 may be suitably altered in shapes. For example, thetwo-resonance antenna device 31 may be formed by forming the supportmember 33 in a spherical shape and then adhering the support member 33on the base member which is formed in a shape conforming to that of thesupport member. Moreover, in order to obtain more than three accurateresonant frequencies, the base member 3 may be separately provided withthe other conductor in addition to the ground conductor 5, the firstantenna element 7 and the second antenna element 9.

FIG. 12A is a view illustrating a first modified form of thetwo-resonance antenna 1 of the present embodiment. A two-resonanceantenna 1A comprises the base member 3, the ground conductor 5, thefirst antenna element 7, the second antenna element 9 and an insulationlayer 40. A difference between the two-resonance antenna 1 and thetwo-resonance antenna 1A resides in structure in which a portion of asurface of the two-resonance antenna 1A is covered with the thininsulation layer 40, and both antennas are the same in other structure.More particularly, the insulation layer 40 is covered over the basemember 3, the first antenna element 7 except for the first connectingportion 7C, the second antenna element 9, and the ground conductor 5except for the second connecting portion 5B. Also, the insulation layer40 may be suffice to be covered over at least the first antenna element7 except for the first connecting portion 7C, the second antenna element9 and the ground conductor 5 except for the second connecting portion5B.

FIG. 12B is a view illustrating a second modified form of thetwo-resonance antenna 1 of the present embodiment. A difference betweenthe two-resonance antenna 1B and the two-resonance antenna 1A resides instructure in which the first connecting portion 7C and the secondconnecting portion 5B are not located along the Y-axis, and bothantennas are the same in other structure. Also, the first connectingportion 7C and the second connecting portion 5B are arranged in such astructure as a result of impedance adjustment made between thetwo-resonance antenna 1B and the coaxial cable 11.

The two-resonance antennas 1A, 1B have advantageous features listedbelow.

Due to provision of the insulation layer 40, the ground conductor 5, thefirst antenna element 7 and the second antenna element 9 become hard tobe damaged.

Painting the insulation layer 40 one color and the base member 3 anothercolor allows the positions of the first connecting portion 7C and thesecond connecting portion 5B to be easily discriminated from each other.

Upon provision of the insulation layer 40, since the two-resonanceantennas 1A, 1B can directly contact with the other members, no needarises where a separate insulation member is provided in a case wherethe two-resonance antennas 1A, 1B are mounted in a radio communicationapparatus.

FIG. 12C is a view illustrating a third modified form of thetwo-resonance antenna 1 of the present embodiment. A difference betweenthe two-resonance antenna 1C and the two-resonance antenna 1 resides instructure in which the ground conductor 5 has the same width as thefirst antenna element 7 and is located so as to extend along the X-axisfrom one end to the other end of the base member 3, and both antennasare entirely the same in other structure.

The two-resonance antenna according to the present invention can besuitably altered without being limited by the various embodimentsdescribed above.

There is no need for the ground conductor 5, the first antenna element 7and the second antenna element 9 to be disposed on one surface of thebase member 3, and second antenna element 9 may be located on a rearsurface of the base member 3.

The ground conductor 5 and the first antenna element 7 may be connectedto each other so as not to form the slit portion 6 and, further, thesecond antenna element 9 may not be disposed in the slit portion 6. Thatis, the second antenna element 9 may be disposed on the base member 3 soas not to directly connect to the ground conductor 5 and the firstantenna element 7 after the base member 3 is formed with the groundconductor 5 with a large surface area and then one end of the firstantenna element 7 is connected to one end of the ground conductor 5.

In place of the coaxial cable 11, a cable in which two lead wires extendin parallel to each other may be employed.

It may be designed such that a plurality of antenna elements areadditionally disposed on the surface of the base member 3 such thatthese additional antenna elements do not directly connect to the groundconductor 5, the first antenna element 7 and the second antenna element9, whereby the additional antenna elements resonate at more than twofrequencies.

Second Embodiment

FIG. 13 is a plan view of a two-resonance antenna 41. In the presentembodiment, a major axis and a minor axis of a base member 43 areassigned to an X-axis and a Y-axis, respectively, and the X-axis and theY-axis perpendicularly cross each other.

The two-resonance antenna 41 is a monopole antenna formed in a filmshape and comprises the base member 43, a first antenna element 45, asecond antenna element 47 and an impedance adjustment element 49. Thebase member 43 is formed of a rectangular thin plate with flexibilityand is made of dielectric material such as resin of polyamide system.The first antenna element 45, the second antenna element 47 and theimpedance adjustment element 49 are formed on a surface of the basemember 43.

The first antenna element 45 is a conductor formed in a strip shape witha first radiating portion 45A, a second radiating portion 45B and aninterconnecting portion 45C. The first radiating portion 45A is disposedalong the X-axis. The second radiating portion 45B is disposed on a +Yside with respect to the first radiating portion 45A and along theX-axis. A distal end 45G of the second radiating portion 45B terminateson a +X side with respect to a distal end 45F of the first radiatingportion 45A. The interconnecting portion 45C is disposed along theY-axis and provides electrical connection between a base end 45E of thefirst radiating portion 45A and a base end portion 45D of the secondradiating portion 45B. With such an arrangement, a slit portion 46having an open at one end thereof is formed on the base member 43.

The second antenna element 47 is formed in a strip shape. The secondantenna element 47 is disposed in the slit portion 46 along the X-axis.A distal end 47A of the second antenna element 47 terminates on a +Xside with respect to the distal end 45F of the first radiating portion45A and on a −X side with respect to the distal end 45G of the secondradiating portion 45B.

The impedance adjustment element 49 is formed in a strip shape. Theimpedance adjustment element 49 is disposed in the slit portion 46 alongthe X-axis and between the second radiating portion 45B of the firstantenna element 45 and the second antenna element 47. A distal end 49Aof the impedance adjustment element 49 terminates on a +X side withrespect to the distal end 45G of the second radiating portion 45B of thefirst antenna element 45 and on a +X side with respect to the distal end47A of the second antenna element 47. A base end portion 49B of theimpedance adjustment element 49 terminates on +X side with respect to abase end portion 47B of the second antenna element 47. Also, theimpedance adjustment element 49 may be located on a rear surface of thebase member 43.

The antenna elements used by the two-resonance antenna 41 decrease inlength in the order corresponding to the first radiating portion 45A ofthe first antenna element 45, the second antenna element 47, the secondradiating portion 45B of the first antenna element 45 and the impedanceadjustment element 49. Here, it is noted that lengths of the secondradiating portion 45B of the fist antenna element 45 and the impedanceadjustment element 49 can be varied so as to adjust a resonancefrequency of the two-resonance antenna 41.

As shown in FIG. 14, actual sizes of the antenna elements used in thepresent invention are as follows. The first radiating portion 45A of thefirst antenna element 45 is a conductor having 1 mm in width and 54 mmin length. The second radiating portion 45B of the first antenna element45 is a conductor having 1 mm in width and 20 mm in length. Theinterconnecting portion 45C of the first antenna element 45 is aconductor having 1 mm in width and 3 mm in length. The second antennaelement 47 is a conductor having 1 mm in width and 21 mm in length andis disposed in the slit portion 46 at about 7 mm distance from theinterconnecting portion 45C of the first antenna element 45. Theimpedance adjustment element 49 is a conductor having 1 mm in width and11 mm in length and is disposed at about 7 mm distance from theinterconnecting portion 45C of the first antenna element 45. Here, it isnoted that the impedance adjustment element 49 may be displaced in thedirection of the X-axis with respect to the second antenna element 47within the range of about 3 mm.

The coaxial cable 11 has the same structure as that of the coaxial cableemployed in the first embodiment. Also, in place of the coaxial cable11, a cable in which two lead wires extend in parallel to each other maybe employed.

As shown in FIG. 13, a first connecting portion 51 is formed on a partof the second radiating portion 45B of the first antenna element 45 inorder to electrically connect the first antenna element 45 to the centerconductor 13 of the coaxial cable 11 by direct-current electricity. Afirst contact portion 53 is formed on a part of the impedance adjustmentelement 49 in order to fix the impedance adjustment element 49 to thecovering material 15 of the coaxial cable 11 by contact or an adhesive.The impedance adjustment element 49 is isolated from the centerconductor 13 and the outer conductor 17 of the coaxial cable 11 by thecovering material 15 of the coaxial cable 11. A second connectingportion 55 is formed on a part of the second antenna element 47 in orderto electrically connect the second antenna element 47 to the outerconductor 17 of the coaxial cable 11 by direct-current electricity. Asecond contact portion 57 is formed on a part of the first radiatingportion 45A of the first antenna element 45 in order to fix the firstantenna element 45 to the sheath 18 of the coaxial cable 11 by contactor an adhesive. The first radiating portion 45A is isolated from thecenter conductor 13 and the outer conductor 17 of the coaxial cable 11by the sheath 18 of the coaxial cable 11. The first connecting portion51, the second connecting portion 55, the first contact portion 53 andthe second contact portion 57 are located on a straight line along theY-axis.

The center conductor 13 exposed at a terminal portion of the coaxialcable 11 is connected to the first connecting portion 51 by soldering.The center conductor 13 covered with the covering material 15 is fixedto the first contact portion 53 by contact or an adhesive. Since thecenter conductor 13 is not directly connected to the impedanceadjustment element 49, no electric current flows between the impedanceadjustment element 49 and the center conductor 13 even when applied withdirect-current electricity. The outer conductor 17 exposed from thecoaxial cable 11 is connected to the second connecting portion 55 bysoldering. The outer conductor 17 covered with the sheath 18 is fixed tothe second contact portion 57 by contact or an adhesive. Since the outerconductor 17 is not directly connected to the first radiating portion45A of the first antenna 45, no electric current flows between the firstradiating portion 45A and the outer conductor 17 even when applied withdirect-current electricity.

The first antenna element 45 is capacitively coupled with the secondantenna element 47 and the impedance adjustment element 49 via the basemember 43. This arrangement is equivalent to an arrangement in which thefirst antenna element 45 is connected to the second antenna element 47and the impedance adjustment element 49 via a capacitor. Accordingly, ifalternating-current electricity is applied to the center conductor 13 ofthe coaxial cable 11, electric current flows between the first antennaelement 45 and the second antenna element 47 and between the firstantenna element 45 and the impedance adjustment element 49.

First resonance of the two-resonance antenna 41 is generated by electriccurrent distributed on the first antenna element 45. Second resonance ofthe two-resonance antenna 41 is generated by electric currentdistributed on the second antenna element 47. Since the impedanceadjustment element 49 serves to adjust impedance between thetwo-resonance antenna 41 and the coaxial cable 11 so as to decrease avalue of the VSWR, a plurality of band widths with a frequency in whichthe VSWR has a value less than “2” are secured.

The two-resonance antenna 41 thus constructed has a VSWR characteristicshown in FIG. 15 and a radiating characteristic shown in FIG. 16A.

A graph indicated by a broken line in FIG. 15 represents the VSWRcharacteristic of the two-resonance antenna 1. A graph indicated by asolid line in FIG. 15 represents the VSWR characteristic of thetwo-resonance antenna 41. In FIG. 15, there are two band widthsappearing at two regions with a frequency in which the VSWR has a valueless than “2”. One of these regions lies in a value ranging from 2.3 GHzto 2.6 GHz. The other of these regions lies in a value ranging from 4.5GHz to 5.9 GHz. Accordingly, the band widths correspond to a range ofapproximately 300 MHz at 2 GHz band and a range of approximately 1400MHz at 5 GHz band.

With the two-resonance antenna 1, the VSWR value exhibits the minimalvalue at a frequency of approximately 5.15 GHz, and a frequency range(frequency band) in which the VSWR value is less than “2” lies between5.1 GHz and 5.2 GHz. With the two-resonance antenna 41, the VSWR valueexhibits the minimal values at frequencies of approximately 4.9 GHz and5.8 GHz, and a frequency range in which the VSWR value is less than “2”lies between 4.5 GHz and 5.9 GHz, resulting in an increase in thefrequency range in which the VSWR value is less than “2”. Here, it isnoted that the increase in the frequency range set forth above is basedon one factor in which the above-described minimal values are close toeach other. The two-resonance antenna 41 generates the resonantfrequency in the vicinity of 2 GHz substantially similar to that of thetwo-resonance antenna 1.

As shown in FIG. 16A, in 2 GHz and 5 GHz bands, the radiatingcharacteristic of the two-resonance antenna 41 has vertical polarizedwaves forming main polarized waves with shapes nearly equal to circularconfigurations and has high-gain availabilities. Accordingly, thetwo-resonance antenna 41 has omnidirection and high-gain availabilitythat are desired characteristics of the antenna.

The two-resonance antenna 41 has advantageous features listed below.

The first resonant frequency and the second resonant frequency can befreely set to arbitrary values, respectively, because the first antennaelement 45 on which the first resonant frequency is generated and thesecond antenna element 47 on which the second resonant frequency isgenerated are disposed to be independent from each other.

Impedance adjustment between the two-resonance antenna 41 and thecoaxial cable 11 can be easily performed because the impedanceadjustment element 49 can be disposed to be independent from the firstantenna element 45 and the second antenna element 47.

Impedance adjustment between the two-resonance antenna 41 and thecoaxial cable 11 can be easily performed because the first connectingportion 51, the second connecting portion 55, the first contact portion53 and the second contact portion 57 can be set to respective positionsindependent from one another.

The coaxial cable 11 can be easily fixed to the two-resonance antenna 41because the first connecting portion 51, the second connecting portion55, the first contact portion 53 and the second contact portion 57 aredisposed on the surface of the base member 43. In addition, the coaxialcable 11 can be easily fixed to the two-resonance antenna 41 withoutbending because the first connecting portion 51, the second connectingportion 55, the first contact portion 53 and the second contact portion57 are linearly located.

The antenna can be realized in a miniaturized and thin structure becausethe two-resonance antenna 41 is fabricated by forming the split portion46 which opens at one end thereof on the base member 43 and locating therectangular second antenna element 47 and the rectangular impedanceadjustment element 49 in the slit portion 46 dependent on the shape ofthe first antenna element 45.

Electrical capacitances between the second antenna element 47 and thefirst radiating portion 45A and between the second antenna element 47and the second radiating portion 45B can be easily ensured such thatthey have respective large values because the second antenna element 47is formed in an elongated state in substantially parallel to and alongthe first radiating portion 45A and the second radiating portion 45B ofthe first antenna element 45 and is disposed between the first radiatingportion 45A and the second radiating portion 45B of the first antennaelement 45.

Noises occurring in the two-resonance antenna 41 are absorbed by theouter conductor 17 because the coaxial cable 11 in which the outerconductor 17 is disposed outside the center conductor 13 is employed asthe electric power supply line for the antenna.

A simplification in an antenna structure and reduction in manufacturingcost can be realized because the two-resonance antenna 41 ismanufactured by forming the first antenna element 45, the second antennaelement 47 and the impedance adjustment element 49 in thin film metallicelements on the surface of the base member 3 made of the dielectricmaterial of the polyamide system.

A plurality of resonant frequencies can be easily generated at 5 GHzband by means of the two-resonance antenna 41 because the two-resonanceantenna 41 has a wide band width at 5 GHz band. In addition, thetwo-resonance antenna 41 can generate a resonant frequency at 2 GHz bandas in the case of the two-resonance antenna 1.

When the two-resonance antenna 41 is applied to a notebook-sized PC asan antenna for a wireless LAN compatible with two-frequencies, thetwo-resonance antenna 41 can be installed on an LCD section and a cornerportion of a casing of the notebook-sized PC, and a support member (seeFIGS. 17, 18, 19).

A thin insulation layer 59 may be covered on a portion of the surface ofthe two-resonance antenna 41 as a two-resonance antenna 41A (see FIG.20). More specifically, the insulation layer 59 covers the base member43, the first antenna element 45 except for the first connecting portion51, the second antenna element 47 except for the second connectingportion 55 and the impedance adjustment element 49.

Third Embodiment

FIG. 21 is a plan view of a two-resonance antenna 61. In the presentembodiment, a major axis and a minor axis of a base member 63 areassigned to an X-axis and a Y-axis, respectively, and the X-axis and theY-axis perpendicularly cross each other.

The two-resonance antenna 61 and the two-resonance antenna 41 of thesecond embodiment are different in structure in which the impedanceadjustment element 49 is removed from the slit portion 46 and areentirely identical in other structure.

The coaxial cable 11 has the same structure as that of the coaxial cableemployed in the first embodiment. Also, in place of the coaxial cable11, a cable in which two lead wires extend in parallel to each other maybe employed.

First resonance of the two-resonance antenna 61 is generated by electriccurrent distributed on the first antenna element 45. Second resonance ofthe two-resonance antenna 61 is generated by electric currentdistributed on the second antenna element 47.

The two-resonance antenna 61 thus constructed has a VSWR characteristicshown in FIG. 22 and a radiating characteristic shown in FIG. 23A.

A graph indicated by a broken line in FIG. 22 represents the VSWRcharacteristic of the two-resonance antenna 1. A graph indicated by asolid line in FIG. 22 represents the VSWR characteristic of thetwo-resonance antenna 61. In FIG. 22, there are two band widthsappearing at two regions with a frequency in which the VSWR has a valueless than “2”. One of these regions lies in a value ranging from 2.2 GHzto 2.6 GHz. The other of these regions lies in a value ranging from 4.5GHz to 6.0 GHz. Accordingly, the band widths correspond to a range ofapproximately 400 MHz at 2 GHz band and a range of approximately 1500MHz at 5 GHz band.

With the two-resonance antenna 1, the VSWR value exhibits the minimalvalue at a frequency of approximately 5.15 GHz, and a frequency range(frequency band) in which the VSWR value is less than “2” lies between5.1 GHz and 5.2 GHz. With the two-resonance antenna 61, the VSWR valueexhibits the minimal values at frequencies of approximately 4.7 GHz and5.3 GHz, and a frequency range in which the VSWR value is less than “2”lies between 4.5 GHz and 6.0 GHz, resulting in an increase in thefrequency range in which the VSWR value is less than “2”. Here, it isnoted that the increase in the frequency range set forth above is basedon one factor in that the above-described minimal values are close toeach other. The two-resonance antenna 61 generates the resonantfrequency in the vicinity of 2 GHz substantially similar to that of thetwo-resonance antenna 1.

As shown in FIG. 23A, in 2 GHz and 5 GHz bands, the radiatingcharacteristic of the two-resonance antenna 61 has vertical polarizedwaves forming main polarized waves with shapes nearly equal to circularconfigurations and has high-gain availabilities. Accordingly, thetwo-resonance antenna 61 has omnidirection and high-gain availabilitythat are desired characteristics of the antenna.

A plurality of resonant frequencies can be easily generated at 5 GHzband by means of the two-resonance antenna 61 because the two-resonanceantenna 61 has a wide band width at 5 GHz band. In addition, thetwo-resonance antenna 61 can generate a resonant frequency at 2 GHz bandas in the case of the two-resonance antenna 1.

When the two-resonance antenna 61 is applied to a notebook-sized PC asan antenna for a wireless LAN compatible with two-frequencies, thetwo-resonance antenna 61 can be installed on an LCD section and a cornerportion of a casing of the notebook-sized PC, and a support member likethe two-resonance antenna 1 of the first embodiment.

The two-resonance antenna 61 has the substantially same features asthose of the two-resonance antenna 1 and, further, a thin insulationlayer may be covered on a portion of the surface of the two-resonanceantenna 1.

Fourth Embodiment

FIG. 24 is a plan view of a two-resonance antenna 81. In the presentembodiment, a major axis and a minor axis of a base member 83 areassigned to an X-axis and a Y-axis, respectively, and the X-axis and theY-axis perpendicularly cross each other.

The two-resonance antenna 81 and the two-resonance antenna 41 of thesecond embodiment are different in structure in where a first antennaelement 89 and a second antenna element 91 are formed on a rear surfaceof the base member 83 and second antenna elements 87, 91 areelectrically connected to each other by means of a through-hole 93, andare entirely identical in other structure.

The through-hole 93 is formed at a central area of the base member 83.Under a condition where a first antenna element 85 is formed on a frontsurface of the base member 83 and the first antenna element 89 is formedon the rear surface of the base member 83, the first antenna element 85and the first antenna element 89 are located in a mutually pointsymmetry with respect to the through-hole 93. Under a condition wherethe second antenna element 87 is formed on the front surface of the basemember 83 and the second antenna element 91 is formed on the rearsurface of the base member 83, the second antenna element 87 and thesecond antenna element 91 are located in a mutually point symmetry withrespect to the through-hole 93.

The center conductor of the coaxial cable is electrically connected to asecond radiating portion 85B of the first antenna element 85 through afirst connecting portion by direct-current electricity. The outerconductor of the coaxial cable is electrically connected to the secondantenna element 87 through a second connecting portion by direct-currentelectricity. The sheath of the coaxial cable is fixed to a firstradiating portion 85A of the first antenna element 85 through a contactportion by contact or an adhesive. The first radiating portion 85A isisolated from the center conductor and the outer conductor of thecoaxial cable by the sheath of the coaxial cable. The outer conductor ofthe coaxial cable is electrically connected to the second antennaelement 91 through the second connecting portion, the second antennaelement 87 and the through-hole 93. Since the coaxial cable is connectedto only the front surface of the base member 83, the first antennaelement 89 is isolated from the center conductor and the outer conductorof the coaxial cable.

The coaxial cable has the same structure as that of the coaxial cableemployed in the first embodiment. Also, in place of the coaxial cable, acable in which two lead wires extend in parallel to each other may beused.

By adjusting the first antenna elements 85, 89 and the second antennaelements 87, 91 in shape and size so as to allow a mutually positionalrelationship to remain in a suitable status, the two-resonance antenna81 generates four resonant frequencies.

For example, if the first antenna element 85 and the second antennaelement 87 are disposed on the front surface of the base member 83 andthe first antenna element 89 and the second antenna element 91 aredisposed on the rear surface of the base member 83 so as to allow tworesonant frequencies and the other two resonant frequencies to begenerated at 2 GHz band and 5 GHz band, respectively, the resonantfrequencies are generated in a wide range at 2 GHz and 5 GHz bands byusing only one two-resonance antenna 81.

Here, the first antenna element 85 and the first antenna element 89 donot need to be identical in shape. Similarly, the second antenna element87 and the second antenna element 91 do not need to be identical inshape.

When the two-resonance antenna 81 is applied to a notebook-sized PC asan antenna for a wireless LAN compatible with two-frequencies, thetwo-resonance antenna 81 can be installed on an LCD section and a cornerportion of a casing of the notebook-sized PC, and a support member likethe two-resonance antenna 1 of the first embodiment.

The two-resonance antenna 81 has the substantially same features asthose of the two-resonance antenna 1 and, further, a portion of thesurface of the two-resonance antenna 81 can be covered with a thininsulation layer.

INDUSTRIAL APPLICABILITY

A simplification in an antenna structure and reduction in manufacturingcost can be realized because the antenna of the present invention can beplaced in a narrow space and easily obtain a plurality of accurateresonant frequencies each which belongs to a separate frequency band.

1. An antenna comprising: a thin plate-like base member (3) made ofdielectric material; a ground conductor (5) formed of a thin-film shapedand rectangular conductor and disposed on the base member (3); a firstantenna element (7) formed of a thin-film shaped and L-shaped conductor,having one end connected to one end of the ground conductor (5) anddisposed on the base member (3); and a second antenna element (9) formedof a thin-film shaped and rectangular conductor and disposed on the basemember (3) without being directly connected to the ground conductor (5)and the first antenna element (7).
 2. The antenna according to claim 1,wherein a first resonance is generated by electric current distributedon the first antenna element (7) and a second resonance is generated byelectric current distributed on the second antenna element (9).
 3. Theantenna according to claim 1, wherein the ground conductor (5), thefirst antenna element (7) and the second antenna element (9) aredisposed on one surface of the base member (3).
 4. The antenna accordingto claim 3, wherein a slit portion (6) opening at a part thereof isformed on the base member (3) by combining the ground conductor (5) andthe first antenna element (7) and the second antenna element (9) isdisposed in the slit portion (6).
 5. The antenna according to claim 1,further comprising: a first connecting portion (7C) formed on the firstantenna element (7) in order to electrically connect the first antennaelement (7) to a first conductor (13) of a cable (11); a contact portion(9A) formed on the second antenna element (9) in order to electricallyconnect the second antenna element (9) to a second conductor (17) of thecable (11) via dielectric member (18); and a second connecting portion(5B) formed on the ground conductor (5) in order to electrically connectthe ground conductor (5) to the second conductor (17) of the cable (11).6. The antenna according to claim 5, wherein a thin insulation layer(40) is covered over surfaces of the first antenna element (7) exceptfor the first connecting portion (7C), the second antenna element (9)and the ground conductor (5) except for the second connecting portion(5B).
 7. The antenna according to claim 5, wherein the cable (11), thefirst conductor (13), the second conductor (17) and the dielectricmember (18) are a coaxial cable, an inner conductor of the coaxialcable, an outer conductor of the coaxial cable and a sheath of thecoaxial cable, respectively.
 8. The antenna according to claim 7,wherein a film-like dielectric member is disposed between the contactportion (9A) and the sheath of the coaxial cable.
 9. The antennaaccording to claim 1, wherein the base member (3) has flexibility. 10.The antenna according to claim 9, wherein the ground conductor (5), thefirst antenna element (7) and the second antenna element (9) haveflexibilities.
 11. The antenna according to claim 10, furthercomprising: a support member (33) made of non-conductor and fixedlysecuring the base member (3).
 12. The antenna according to claim 11,wherein the support member (33) comprises: an upper end portion (35)extending to one direction; a lower end portion (39) disposed inparallel to the upper end portion (35); and an interconnecting portion(37) having one end vertically connected to one end (35B) of the upperend portion (35) and the other end vertically connected to one end (39B)of the lower end portion (39).
 13. The antenna according to claim 1,wherein the base member (3) is mounted on an LCD section (20) of anotebook-sized PC (19).
 14. The antenna according to claim 1, whereinthe base member (3) is mounted on a corner area of a casing (21) of anotebook-sized PC (19).
 15. The antenna according to claim 1, whereinthe ground conductor (5), the first antenna element (7) and the secondantenna element (9) are formed on the base member (3) by means of atleast one of an etching technique and a screen printing technique. 16.An antenna comprising: a thin plate-like base member (43) made ofdielectric material; a first antenna element (45) formed of a thin-filmshaped conductor and disposed on the base member (43) so as to form aslit portion (46) opening at a part thereof; a second antenna element(47) formed of a thin-film and strip shaped conductor and disposed inthe slit portion (46); and an impedance adjustment element (49) formedof a thin-film and strip shaped conductor and disposed between one side(45B) of the first antenna element (45) and the second antenna element(47) in the slit portion (46).
 17. The antenna according to claim 16,wherein a first resonance is generated by electric current distributedon the first antenna element (45), a second resonance is generated byelectric current distributed on the second antenna element (47) andimpedance is adjusted corresponding to a shape and arrangement locationof the impedance adjustment element (49).
 18. The antenna according toclaim 16, wherein the first antenna element (45), the second antennaelement (47) and the impedance adjustment element (49) are disposed onone surface of the base member (43).
 19. The antenna according to claim18, wherein the first antenna element (45) comprises: a first radiatingportion (45A) formed in a strip shape; a second radiating portion (45B)formed in a strip shape and disposed in parallel to the first radiatingportion (45A); and an interconnecting portion (45C) having one endvertically connected to one end (45E) of the first radiating portion(45A) and the other end vertically connected to one end (45D) of thesecond radiating portion (45B), the second antenna element (47) isdisposed between the first radiating portion (45A) and the secondradiating portion (45B) and in parallel to the first radiating portion(45A), and the impedance adjustment element (49) disposed between thesecond radiating portion (45B) and the second antenna element (47) andin parallel to the second radiating portion (45B).
 20. The antennaaccording to claim 19, wherein the first radiating portion (45A) islonger than the second antenna element (47) and the second antennaelement (47) is longer than the second radiating portion (45B) and theimpedance adjustment element (49).
 21. The antenna according to claim16, further comprising: a first connecting portion (51) formed on thesecond radiating portion (45B) in order to electrically connect thesecond radiating portion (45B) of the first antenna element (45) to afist conductor (13) of a cable; a first contact portion (53) formed onthe impedance adjustment element (49) in order to contact the impedanceadjustment element (49) to the first conductor (13) of the cable (11)covered with a covering material (15); a second connecting portion (55)formed on the second antenna element (47) in order to electricallyconnect the second antenna element (47) to a second conductor (17) ofthe cable (11); and a second contact portion (57) formed on the firstradiating portion (45A) in order to contact the first radiating portion(45A) of the first antenna element (45) to the second conductor (17) ofthe cable (11) via a dielectric member (18).
 22. The antenna accordingto claim 21, wherein a thin insulation layer (59) is covered oversurfaces of the first antenna element (45) except for the firstconnecting portion (51), the second antenna element (47) except for thesecond connecting portion (55) and the impedance adjustment element(49).
 23. The antenna according to claim 21, wherein the cable (11), thefirst conductor (13) and the second conductor (17) are a coaxial cable,an inner conductor of the coaxial cable and an outer conductor of thecoaxial cable, respectively.
 24. The antenna according to claim 16,wherein the base member (43) has flexibility.
 25. The antenna accordingto claim 24, wherein the first antenna element (45), the second antennaelement (47) and the impedance adjustment element (49) haveflexibilities.
 26. The antenna according to claim 10, furthercomprising: a support member (33) made of non-conductor and fixedlysecuring the base member (43).
 27. The antenna according to claim 26,wherein the support member (33) comprises: an upper end portion (35)extending to one direction; a lower end portion (39) disposed inparallel to the upper end portion (35); and an interconnecting portion(37) having one end vertically connected to one end (35B) of the upperend portion (35) and the other end vertically connected to one end (39B)of the lower end portion (39).
 28. The antenna according to claim 16,wherein the base member (43) is mounted on an LCD section (20) of anotebook-sized PC (19).
 29. The antenna according to claim 16, whereinthe base member (43) is mounted on a corner area of a casing (21) of anotebook-sized PC (19).
 30. The antenna according to claim 16, whereinthe first antenna element (45), the second antenna element (47) and theimpedance adjustment element (49) are formed on the base member by meansof at least one of an etching technique and a screen printing technique.31. An antenna comprising: a thin plate-like base member (43) made ofdielectric material; a first antenna element (45) formed of a thin-filmshaped conductor and disposed on the base member (43) so as to form aslit portion (46) opening at a part thereof; and a second antennaelement (47) formed of a thin-film and strip shaped conductor anddisposed in the slit portion (46).
 32. The antenna according to claim31, further comprising: a first rear surface antenna element (89) formedof a thin-film shaped conductor and disposed on the other surface of thebase member (83) so as to form a rear surface slit portion opening at apart thereof; and a second rear surface antenna element (91) formed of athin-film and strip shaped conductor, disposed in the rear surface slitportion and electrically connected to the second antenna element (47,87).
 33. The antenna according to claim 32, wherein the first rearsurface antenna element (89) comprises: a first rear surface radiatingportion formed in a slip-shape; a second rear surface radiating portionformed in a slip-shape and disposed in parallel to the first rearsurface radiating portion; and a rear surface interconnecting portionconnecting one end of the first rear surface radiating portion and oneend of the second rear surface radiating portion, and the second rearsurface antenna element (91) is disposed between the first rear surfaceradiating portion and the second rear surface radiating portion and inparallel to the first rear surface radiating portion.